Abstract
To achieve efficient forward osmosis (FO) for desalination, thermal-responsive hydrogels were synthesized by polymerization of N-isopropylacrylamide (NIPAM) in the presence of ionic polyglutamic acid (γ-PGA) and pore-forming polyethylene glycol (PEG). The equilibrium swelling ratio (ESR) and deswelling behaviour of PNIPAM/γ-PGA/PEG hydrogels were investigated at a series of dosages of reactants (γ-PGA, PEG, initiator and cross-linker). The PNIPAM/γ-PGA/PEG hydrogel revealed effective deswelling response at low temperature (35.20 °C). The highest ESR was 94.76 g/g, and the fastest dewatering ratio could reach 97.64% within 30 min. The optimal mass ratio of comonomers (NIPAM, γ-PGA and PEG), crosslinker and initiator was fixed at 1:0.2:1:0.01:0.01 determined by the response surface method (RSM). It was also found by RSM that the ESR was significantly dependent on cross-linker and the interaction between initiator and γ-PGA. The optimal hydrogel was examined as draw agent, employing deionized (DI) water and 0.05, 0.1 and 0.2 wt% NaCl solution as the feed, which showed the enhanced water fluxes at 1.99, 1.65, 1.31 and 1.08 LMH in initial 0.5 h. In addition, the hydrogel showed promising recyclability in term of water flux in three cycles.
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